Extraction centrifuge



A ril 9, 1968 3. HULTSCH ETAL 3,376,978

I EXTRACTION CENTRIFUGE Filed Aug. 17, 1966 5 $heetsSheet-'L Attorney April 1968 G. HULTSCH ETAL v3,376,978

EXTRACTION CENTR IFUGE Filed Aug. 17, 1966 3 Sheets-Sheet Attorney April 9, G HULTSCH ETAL EXTRACTION CENTR IFUGE Filed Aug. 17, 1966 5 Sheets-Sheet Fig. 4

GUnfher Hulfsch A lbrechf Beck l.\ L.\ l was.

Attorney United States Patent K 8, 15 Claims. (Cl. 210-375) ABSTRACT OF THE DISCLOSURE Extraction centrifuge wherein a spreader is axially reciprocated to deposit a filtrand on a perforated wall of the drum, the spreader moving substantially in synchronism with an unloader, such as a scraper, which precedes the spreader outlet during a forward stroke, both the unloader and the spreader being ineffectual during a subsequent return stroke.

Our present invention relates to an extraction centrifuge of the type wherein a drum, having a perforated peripheral wall, is rotatable about a (usually horizontal) axis at high enough speeds to separate a filtrate from a filtrand, e.g. a mother liquor from sirup in the sugar industry or juices from various botanicals.

In the operation of such centrifuges, the material to be treated is spread as uniformly as possible over the inner peripheral drum surface from which, after extraction of the fluids, the remaining solids are removed except for a residual layer or cake through which the liquor from the subsequently treated matter is filtered. This removal of solids is usually carried out with the aid of an axially reciprocable unloader tool, such as a scraper knife, designed to exert only slight radial pressure upon the residual cake so as to avoid excessive densification v thereof.

In conventional machinery of this type it is the practice to operate discontinuously in two distinct stages respectively involving spreading (with immediately following extraction) and unloading. This mode of operation is time-consuming and frequently requires the use of several drums to handle a load which, in terms of filtering action alone, would be well Within the capacity of a single drum.

It is, therefore, the general object of our present invention to prOvide means in such machinery for rapidly and substantiallyconcurrently performing the two operations referred to so that at least a major part ofthe available drum surface is always covered with fresh filtrand whereby extraction proceeds continuously, with consequent maximum utilization of the centrifuging capacity of the equipment.

This object is realized in accordance with our invention, by the provision of drive means for reciprocating a scraper knife or other unloader along the inner drum periphery in axially spaced relationship with reference to the outlet of an associated spreader, this outlet being periodically displaceable in a predetermined axial direction within the drum so as to trail the unloader during a forward stroke of the latter by a small distance whereby fresh, filtrand is deposited on the drum wall promptly upon removal of the spent solids. Upon completing its working stroke, during which it led the spreader outlet, the unloader-is deactivated by a suitable controller so as to perform its return stroke, preferably at considerably higher speed, in an ineffectual condition in order not to disturb the freshly deposited layer undergoing centrifugation.

The axially displaceable spreader outlet may be constituted by an orifice in a reciprocable spray head which 3,376,978 Patented Apr. 9, 1968 is coupled With the unloader for joint axial displacement within the drum; the flow of filtrand to this head may then be cut off during the joint return stroke so that a new layer is formed on the drum wall only in the wake of the advancing unloader. According to another feature of our invention, however, this outlet is constituted by the lowest point of a substantially helicoidal slot in a horizontal spreader tube rotatably disposed in the lower part of the drum, the tube performing one revolution per reciprocating of the unloader; if the slot extends over less than a full turn, e.g. over an angle of about 270 to 300, no discharge will occur from the tube during a fraction of its rotation which should coincide with the return stroke of the unloader. With certain filtrands especially those not containing solids of a crystalline nature, the rotatable tube may surround or be surrounded by a stationary tube having an axially extending bottom slot which defines the outlet by its intersection with the helicoidal slot of the other tube.

If the unloader is in the form of an otherwise conventional scraper knife, its deactivation during the return stroke may be effected by swinging it, about a pivotal axis parallel to the drum axis, from a generally radial operativ position into a disengaged position, e.g. one offset by from the former. Pursuant to a further feature of our invention, however, the unloader may be a nozzle at the end of a conduit connected to a source of high-pressure gas, this nozzle being advantageously disposed with upward orientation within a funnel-shaped end of a suction pipe serving to carry off dislodged solids.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a longitudinal sectional view of a centrifuge drum embodying the present improvement;

FIG. 1A is a top view of a spreader assembly shown in FIG. 1;

FIG. 2 is a view similar to FIG. 1, showing a modified centrifuge with a different type ofv spreader;

FIG. 3 is a side-elevational view, partlyin section and drawn to a larger scale, of a modification of the spreader shown in FIG. 2;

FIG. 3A is a cross-sectional view taken on the line IIIAIIIA of FIG. 3; and

FIG. 4 is another view similar to FIG. 1, illustrating a different type of unloader.

Reference is first made to the extraction centrifuge illustrated in FIG. 1. This centrifuge comprises a drum 1 with a perforated peripheral wall 3 rotatable at high speeds, by conventional means not shown, about a horizontal axis. The left-hand end of drum 1 is closed by a transverse wall 30, its right-hand end 5 being open except foran annular barrier 48 defining a treatment space adjacent the inner surface of peripheral wall 3 which is lined by a cylindrical screen 47. A filtrand is deposited within that space by a spreader, comprising an axially reciprocable spray head 23, in a peripheral layer 4 which, upon its removai by an axially reciprocable unloader 2, leaves a residual cake 6 adjacent the screen 47. Unloader 2 is shown as a scraper knife with a beveled point which is carried on the free end of a tubular mounting bar 7 formed along its underside into a rack 8 in constant engagement with a pinion 13 of a reversible transmission 15. The housing 32 of this transmission is flexibly supported on the machine frame 37 which has been only partly illustrated and which also carries a chute 11 disposed within drum 1 below the path of unloader 2 in order to intercept detached solids from layer 4 for removal thereof from the drum through its discharge pipe 12.

The outer surface of mounting bar 7 is provided with a groove 9 of generally parallelogrammatic shape, see also FIG. 1A, engaged by a lug 10 rigid with frame 37. The

shape of this groove is so chosen that the unloader knife 2 will be in its illustrated radial position, within a vertical axial plane of the drum, while performing its working stroke from left to right, i.e. from the closed to the open end of the drum, under the control of transmission when the knife reaches the end of this forward stroke, lug 10 by its engagement with the curved left-hand portion 9' of groove 9 rotates the bar 7 about its axis, thereby swinging the knife 2 into a substantially horizontal position in which its point stands clear of the boundary of layer 4. Upon the subsequent reversal on the linear motion of bar 7 and knife 2, the latter is held in an inoperative position until it approaches the end wall whereupon the lug 10, coacting with the opposite flank 9" of groove 9, cams the assembly 2, 7 back into its illustrated working position. The motion of lug 10 relative to groove 9 has been indicated by arrows in FIG. 1A.

The aforedescribed reciprocation of knife 2 is brought about by a motor 14 carried on the transmission housing 32. Keyed to the motor shaft is a pinion 16 which transmits its rotation to pinion 13 either by way of a single gear 17 or through a gear train 18 both mounted on a slidable carriage 19. Gear train 18 consists of three gears, two of them on a common shaft to form a step-up coupling, and with reference to gear 17 reverses as well as accelerates the rotation of pinion 13. More particularly, motor pinion 16 rotates continuously clockwise (as viewed in FIG. 1) so that pinion 13 is driven in the same sense through the intermediary of gear 17, rotating counter-clockwise, when the latter is engaged by a leftward shift of carriage 19 relative to housing 32. Such a leftward shift occurs when, as the knife 2 reaches its extreme left-hand end position, a stop finger 33 entrained by bar 7 strikes the right-hand end of the carriage. At the end of the subsequent working stroke, as the knife is being swung into its ineffectual position, an abutment 38 on bar 7 strikes the projecting left-hand end of carriage 19 to render the gear train 18 effective for a reversal of the knife stroke. Naturally, the teeth of rack 8 must extend over a sufiicient peripheral arc (e.g. a minimum of 90) of tubular bar 7 to remain engaged with the driving pinion 13 in both angular positions of bar 7 and knife 2.

Slidably carried inside bar 7 is a supply tube 20 which terminates in the spray head 23 and has an input end connected to a flexible supply hose 21. A shut-off valve 25, designed to interrupt the flow of filtrand from hose 21 to head 23, is located within the tube 20 and has a rotatable valve stem 26 journaled in a sleeve 27 which tightly embraces the bar 7. Valve stem 26 is integral with a lug 28 positioned to coact with two fixed abutments 34, 36 on machine frame 37; in its righthand position (full lines), into which it isswung by the stop 34 at the end of the leftward return stroke of bar 7, it unblocks the flow of material through tube 20 so that fresh filtrand is deposited by the head 23 in the annular gap of layer 4 cut by the knife 2. At the end of the subsequent working stroke, stop 36 throws the lug 28 into its alternate left-hand position (dot-dash lines) to shut off the supply.

Valve stem 26 traverses a pair of lateral slots 29 in bar 7, the length of these slots enabling a limited relative axial shift between bar 7 and tube 26. The projecting left-hand extremity 22 of tube 20 is surrounded by a coil spring 24 which tends to maintain the head 23 at its greatest distance from knife 2 so that the spray cone issuing from this head will trail the cutting edge of the knife with the necessary spacing. End wall 30 of drum 1 has a recess 31 designed to receive the head 23 in a terminal position of tube 20, the compressibility of spring 24 enabling the knife 2 to be retracted into a limiting position close to wall 30 which is determined by the engagement of sleeve 27 with transmission housing 32. Owing to the relative axial mobility of tube 20 and bar 7, as afforded by the slots 29, recess 31 need not be as deep as would otherwise be necessary in order to facilitate a full sweep of the drum surface 3 by the unloader. If desired, the knife 2 may also be allowed to move out of the open drum end 5 in its inoperative position in order to let the spray head 23 sweep the entire surface of screen 7.

A vibrator 39 is shown connected with knife 2 which has slight transverse mobility with reference to bar 7 so as to oscillate in radial direction when operatively positioncd as shown. The rate of oscillation should be a fraction of a cycle per drum revolution, i.e. not more than half a revolution per cycle, so that the knife point will cut axially spaced grooves into the residual cake 6 to impede a dislocation of the freshly deposited filtrand toward the annular gap 35.

The combination of lug 28 and abutmcnts 34, 36 is, of course, representative of a variety of mechanisms for automaticallyshutting off the flow during alternate reciprocations of the spreader 20, 23 with the aid of a pair of limit switches, whether the controlled valve 25 is located in the axially movable part of the supply conduit, as shown, or in some other part thereofas, for example, in the hose 21. A distributor similar to this spreader may also be provided, if desired, for supplying a diluent or a rinsing fluid to the inner drum periphery by way of a spray head coupled with the unloader 2 for joint axial reciprocation.

In the system of FIG. 2, which is generally similar to that of FIG. 1 and wherein like reference numerals have been used to designate analogous elements, the tubular mounting bar 7 for the unloader knife 2 has been replaced by a solid rod 7a which otherwise functions in the same manner as its counterpart in the system already described. The spreader, however, has been physically separated from the unloader and, in this embodiment, comprises a pair of nested tubes 40, 41, the inner tube 40 being fixedly mounted in the frame 37 and serving as a support for the rotatable outer tube 41. An axially extending slot 42, located at the lowermost generatrix of fixed tube 40, and a helicoidal slot 43, extending for less than a full turn over the periphery of rotatable tube 41, define at their point of intersection an outlet 46 for the discharge of a filtrand delivered to tube 40 via the flexible inlet hose 21. This outlet 46 is progressively and iteratively displaced from left to right as the tube 41 is unidirectionally rotated, in a counterclockwise direction as seen through the open end of drum 1, at a rate of one revolution per reciprocation of unloader assembly 2, 7a; this is accomplished by means of a step-down linkage which comprises a worm 44 on the shaft of motor 14, a worm gear 44" in mesh therewith and a chain drive 45 positively connecting this worm gear with the tube 41. With the slots 42, 43 extending over substantially the full axial length of drum periphery 3, outlet 46 moves virtually from one end of the tube nest 40, 41 to the other during the major part of a revoltuion and then disappears for the remainder of a turn (e.g. a rotation of to with the two slots out of register While the knife 2 performs its ineffectual return stroke at an accelerated rate as previously described. Outer tube 41 is shown to be externally corrugated (e.g. threaded) to prevent the filtrand from distributing itself over the tube surface upon emerging from outlet 46.

With a relatively viscous fluid as the filtrand, the discharge through outlet 46 occurs mainly by gravity for which reason the spreader 40, 41 should be disposed near the drum bottom, as shown. Again, a like assembly may be used for the distribution of other liquids such as a diluent or rinse water; in the case of such less viscous fluids, supplied under pressure, the outlet need not be directed downwardly.

The use of two relatively rotatable tubes with intersecting slots creates difficulties in the case of certain filtrands containing crystalline granules, e.g. sirups in sugar refining. Such relatively refractory solids, which could intrude between the tube walls, may also adversely affect the working point of a scraping knife used for unloading. In FIGS. 3 and 4 we have, therefore, illustrated modified spreading and unloading means, respectively, which are particularly useful for the treatment of molasses or the like without being necessarily limited thereto.

FIG. 3 shows a single tube 55 rotatably journaled in a bearing flange 54 rigid with a wall of machine frame 37. This tube has a helicoidal peripheral slot 57 which is generally similar to slot 43 of the preceding embodiment and extends almost from the closed inner end 59 of the tube to the filtrand inlet formed by a short supply tube 50. The latter tube traverses the forward end of tube 55 and is rotatable therewith as an extension of the stationary feeder hose 21 to which it is coupled through a fixed sleeve 75. An annular baffle 60 surrounds the tube 50 with clearance and defines the inner radius of a peripheral space within which the oncoming filtrand may accumulate along the bottom of the slowly rotating tube 55, any overflow being returned to a compartment 68 formed with a ring of peripheral apertures 61 through which the overflow can enter a stationary annular collector 63; annular surface discontinuities such as ribs 62 flank the apertures 61 to confine this overflow to the collector 63. A drain 64 leads from collector 63. to an inlet port 66 of a pump 65 whose outlet port 67 returns the excess filtrand to the supply tube 50 via sleeve 75.

The filtrand accumulating near the bottom of the main portion 69 of tube 55 tends to escape at the lowest point of slot 57 and is prevented from spreading out along the outer tube surface by two helicoidal surface discontinuities 58, here shown as ribs, flanking the slot. Again, during a minor portion of a revolution the discharge of filtrand will be cut off, with slot 57 located entirely above the filtrand level determined by baffle 60, while the associated unloader performs its return stroke; this has been best illustrated in FIG. 3A where the pool of filtrand is shown at F and the arc spanned by the slot 57 has been indicated at a. The unloader may be of the type described in conjunction with FIGS. 1 and 2 but, advantageously, may also have the shape of an upwardly pointed nozzle 70 as shown in FIG. 4, this nozzle being connected via a pipe 71 and a flexible conduit 77 to a source of high-pressure gas not further illustrated. Nozzle 70 lies within a funnel-shaped entrance end 72 of a discharge pipe 73 which spacedly surrounds the pipe 71 and is axially reciprocable therewith by a mechanism similar to that of FIGS. 1 and 2, including a bar 7b with rack teeth engaged by the drive pinion 13. A lug 78 on bar 7b coacts with a pair of limit switches 79, 80 for alternately opening and closing a solenoid valve 81 in gas line 77 through the intermediary of a, control circuit 82. The inactivation of the unloader 70, 71 through closure of valve 81 occurs, as before, during the accelerated return stroke which again may proceed from right to left as viewed in FIG. 4.

Nozzle 70 may be positioned centrally within the funnel 72 but is preferably somewhat offset from its center in a direction opposite the sense of rotation of drum 1 so that solids dislodged by the gas stream will surely be intercepted by the funnel. These solids are then removed by a pump or blower 74 inserted in pipe 73.

The systems specifically described and illustrated may be modified in various respects. Thus, for example, the slot 57 in FIG. 3 need not be continuous but may be con stituted by an array of closely spaced perforations. The surface discontinuities 58 or 62, shown as ribs, could also have the form of grooves. These and other variations, readily apparent to persons skilled in the art, are deemed to be embraced within the spirit and scope of our invention as defined in the appended claims.

We claim:

1. An extraction centrifuge comprising a rotatable drum with a perforated peripheral wall; spreader means within said drum having an outlet periodically displaceable in a predetermined axial direction along said wall, said spreader means being connected to a source of filtrand for depositing same in a layer on said wall for centrifugal extraction of liquid from said layer and discharge of said liquid through the perforations of said wall; unloader means axially reciprocable within said drum for the detachment of spent solids from said layer; drive means for reciprocating said unloader means dur ing a forward stroke thereof in said predetermined'axial direction substantially at the rate of said outlet and in leading axially spaced relationship therewith whereby detached solids are replaced in the same stroke by fresh filtrand deposited on a residual cake of said layer; and control means coupled with said drive means for rendering said unloader means ineffectual during return strokes in the opposite axial direction; said spreader being provided with means for effectively disconnecting said outlet from said source of filtrand during said return strokes. .2. A centrifuge as defined in claim 1 wherein said spreader means comprises a spray head provided with said outlet and coupled with said unloader means for joint reciprocation by said drive means.

3. A centrifuge as defined in claim 2 wherein the coupling between said head and said unloader means includes spring means tending to maintain a predetermined axial spacing therebetween, said spring means enabling reduction of said axial spacing upon arrival of said head in a limiting position at the end of a return stroke whereby said unloader means can reach parts of said layer deposited at the beginning of the previous forward stroke of said spreader means.

4. A centrifuge as defined in claim 2 wherein Said drum is provided with an end wall having a recess for receiving said head at the end of its return stroke whereby said unloader means can sweep substantially the full length of said peripheral wall.

5. A centrifuge as defined in claim 2 wherein said spreader means comprises a shut-off valve coupled with said head for reciprocable entrainment thereby and abutment means along the path of said Valve engageable therewith for alternately opening and closing same at the end of a return stroke and a forward stroke, respectively.

6. A centrifuge as defined in claim 1 wherein said unloader means comprises a scraper knife with a generally radial operating position, said knife being swingable abouta pivotal axis parallel to the drum axis by said control 'means for disengagement from said layer at the end of a forward stroke and being returnable to said 0peratingposition at the end of a return stroke.

7. A centrifuge as defined in claim 6 wherein said unloader means further includes a vibrator connected with said knife for radially oscillating same in said operating position at a rate of a fraction of an oscillation per drum revolution.

8. A centrifuge as defined in claim 1 wherein said drum has a substantially horizontal axis of rotation and said spreader means comprises a rotatable tube disposed near the drum bottom parallel to said axis, said tube having a substantially helicoidal peripheral outlet-forming slot for the emergence of said filtrand at the bottom thereof, said slot extending over the axial length of said peripheral wall for less than a full turn, said tube being coupled with said drive means for unidirectional rotation about its own axis once per reciprocation of said unloader means for a progressive displacement of the lowest point of said slot along the lowermost generatrix of said tube during a forward stroke of said unloader means and with presentation of an imperforate tube bottom during a return stroke.

9. A centrifuge as defined in claim 1 wherein said unloader means comprises a conduit terminating in a nozzle and connected to a source of high-pressure gas, said unloader means further including a suction pipe having a funnel-shaped end within said drum for receiving detached solids, said nozzle being upwardly oriented within said funnel-shaped end.

10. An extraction centrifuge comprising a rotatable drum with a perforated peripheral wall; spreader means within said drum having an outlet periodically displaceable in a predetermined axial direction along said wall, said spreader means being connected to a source of filtrand for depositing same in a laye on said wall for centrifugal extraction of liquid from said layer and discharge of said liquid through the perforations of said wall; unloader means axially reciprocable within said drum for the detachment of spent solids from said layer; drive means for reciprocating said unloader means during a forward stroke thereof in said predetermined axial direction substantially at the rate of said outlet and in leading axially spaced relationship therewith whereby detached solids are replaced in the same stroke by fresh filtrand deposited on a residual cake of said layer; and control means coupled with said drive means for rendering said unloader means ineffectual during return strokes in the opposite axial direction; said unloader means comprising a scraper knife with a generally radial operating position, said knife being swingable about a pivotal axis parallel to the drum axis by said control means for disengagement from said layer at the end of a forward stroke and being returnable to said operating position at the end of a return stroke; said unloader means further including a vibrator connected with said knife for radially oscillating same in said operating position at a rate of a fraction of an oscillation per drum revolution.

11. An extraction centrifuge comprising a rotatable drum with a perforated peripheral wall; spreader means within said drum having an outlet periodically displacable in a predetermined axial direction along said wall, said spreader means being connected to a source of filtrand for depositing same in a layer on said wall for centrifugal extraction of liquid from said layer and discharge of said liquid through the perforations of said wall; unloader means axially reciprocable within said drum for the detachment of spent solids from said layer; drive means for reciprocating said unloader means during a forward stroke thereof in said predetermined axial direction substantially at the rate of said outlet and in leading axially spaced relationship therewith whereby detached solids are replaced in the same stroke by fresh filtrand deposited on a residual cake of said layer; and control means coupled with said drive means for rendering said unloade means ineflectual during return strokes in the opposite axial direction; said drum having a substantially horizontal axis of rotation and said spreader means comprising a rotatable tube disposed near the drum bottom parallel to said axis, said tube having a substantially helicoidal peripheral outlet-forming slot for the emergence of said filtrand at the bottom thereof, said slot extending over the axial length of said peripheral wall for less than a full turn, said tube being coupled with said drive means for unidirectional rotation about its own axis once per reciprocation of said unloader means for a progressive displacement of the lowest point of said slot along the lowermost generatrix of said tube during a forward strokeof said unl-oader means and with presentation of an imperforate tube bottom during a return stroke.

12. A centrifuge as defined in claim 11 wherein said spreader means further comprises a stationary tube with an axially extending bottom slot in nested relationship with said rotatable tube for defining said outlet at the point of intersection of said slots.

13. A centrifuge as defined in claim 11 wherein said rotatable tube is provided with external surface discontinuities for preventing a spreading of discharged filtrand along said bottom slot.

14. A centrifuge as defined in claim 11 wherein said tube has a closed input end traversed by a supply conduit and is provided internally with an annular baflle which is axially spaced from said closed end and spacedly surrounds an extremity of said conduit whereby excess filtrand delivered by said conduit overflows said battle and enters a tube section between said baflle and said closed end, further comprising feedback means connected with said tube section for returning the overflow to said conduit.

15. A centrifuge as defined in claim 14 wherein said tube section is peripherally apertured along an annular zone, said feedback means including a stationary annular collector enclosing said zone and pump means for delivering said overflow from said collector to said conduit.

References Cited UNITED STATES PATENTS 749,623 l/ 1904 De M archeville 210214 1,453,678 5/1923 Howell 210-377 X 1,827,681 10/1931 Van Der Molen 210375 X 3,038,611 6/1962 OConor et al. 210-376 X FOREIGN PATENTS 559,999 9/1932 Germany.

10,810 1914 Great Britain.

REUBEN FRIEDMAN, Primary Examiner.

I. DE CESARE, Assistant Examiner. 

